<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  <script>
//   //声明一个变量age,并同时里面存放了18这个数据
// let age=18
// //变量里面的数据变化更改为19
// age=19
// //页面输出19
// document.write(age)
  
// let num=20,uname=`张三`,age=19
// document.write(num,uname,age)

 
  console.log(num)
  let num=20
  </script>
</body>
</html>